Self sterilizing hypodermic syringe and method

ABSTRACT

A disposable thermoplastic hypodermic syringe having a hollow metallic needle and thermoplastic body portions at least part of which are formed of temperature calibrated thermoplastic having a full flow liquefaction temperature corresponding to point on the time-death curve for microbial life at which the most resistant spore forms are killed within the time the thermoplastic can be liquefied and resolidified. Heat resistant indicia can be applied to the syringe in a manner to reappear on the solidified thermoplastic mass.

This invention relates to hypodermic syringes and more particularly todisposable hypodermic syringes which after use are capable ofdestruction and verifiable self-sterilization at the point of use and,thereafter, disposal as harmless waste.

BACKGROUND OF THE INVENTION

Disposable hypodermic syringes, one of the most widely used medicaldevices in existence, are also one of the most dangerous to deal with asmedical waste. For obvious reasons their use and disposal are subject toregulation at all levels of government. After professional use they aredeemed Regulated Medical Waste and the cost for their disposal bylicensed handlers under burdens of manifests and regulations which touchevery step of the way from the patients they penetrate to the end ateither licensed incinerators or special refuse centers. Despite theburdensome efforts of control and the consequent expense to society,there are recurring leaks in the system hazardous to the health of many.

Technology for rendering disposable syringes discernably harmless in apractical, cost-effective way at their point of use has been soughtsince the time of their acceptance by the medical industry. The firstattempts involved simply melting down the thermoplastic parts of thesyringes as shown in U.S. Pat. No. 3,958,936, May 25, 1976. Randomlyexposed needles, lack of sterility, and lack of means to verifysterility, even if achieved, rendered the waste dangerous and theprocedure was abandoned. The art of melting down needles was advanced bySwedish Patent No. 8003576-9, published April 1981, which addressed theproblem of randomly exposed needles in the plastic waste by providingsupplemental plastic which melted at or below the syringe meltingtemperature. Sterility and its verifiability remained, however, as a barto acceptance and use.

Color-changing flags in the form of inks, paints and films which changecolor when exposed to desired temperatures are used in connection withsterilization and other thermal procedures. They are widely used as anaid to medical professionals to monitor their autoclaves and dry heatsterilizers. If the color has not changed when the heating cycle ends,an otherwise presentable looking scalpel, for example, is not used andrecalibration of the sterilizer must be ordered. It is a useful tool forsuch purposes but it cannot speak beyond its own surfaces. It cannotverify that the heat it felt reached the needle, nor can it deal withtime functions. A waste manager bent on mischief for example can easilyspot-radiate the patch and proclaim his processed batch sterile atsubstantial savings of time and energy. It does little good, therefore,for reputable manufacturers to place the most reliable color-changingpatch available on medical instruments such as syringes in an attempt toprove the heated or melted down syringes are sterile.

A recent advance in the technology is disclosed in the Applicant's U.S.Pat. Nos. 4,992,217 and 5,078,924 in which verifiable on-sitesterilization as waste of various medical items including disposablesyringes is achieved by the use of special temperature-calibratedthermoplastic formulated, shaped and arranged to achieve liquefaction orphase change only at a temperature and within a time frame which equalsor exceeds the scientifically established and accepted temperature-timedeath curve for the destruction of all known microbial life, includingspore forms, which infect human and other animal life. Sufficientplastic is provided in configurations which insure that molten plasticreaches and covers the needles. The intended purpose of this productcannot be frustrated by either intentional or unintentional error on thepart of the processor. Furthermore, if a manufacturer were to beunreliable in the first place, condemning evidence would survive thetreatment process.

The present invention represents a further advance in the technology ofon-site processing and sterilization of disposable thermoplasticsyringes per se by achieving further overall cost reduction, improvedverification and simplification of the processing procedure, using thebasic technology of U.S. Pat. Nos. 4,992,217 and 5,078,924.

BRIEF SUMMARY OF THE INVENTION

The present invention is based on the teaching of U.S. Pat. Nos.4,992,217 and 5,078,924 that conventional disposable thermoplasticsyringes cannot be reliably or verifiably sterilized by melt-downbecause they are formed of thermoplastic parts which can be melted andthen hardened into a waste mass within a time frame and at temperatureswhich together fall below the time-temperature death curve for microbialcontamination. Verifiable sterilization is, however, shown to beachievable by the use of supplemental temperature-calibratedthermoplastic in the melt-down mass which brings it to a point above thedeath curve.

The present invention provides a new species of the invention whichrenders the syringe, in a melt-down process, capable of verifiableself-sterilization by incorporating temperature-calibrated thermoplasticinto the syringe itself. One preferred syringe part for incorporation isthe plunger stem and thumb-actuator assembly, which undergoes aconspicuous change in geometry upon melt-down while compelling both timeand temperature functions which insure sterility. An unmelted plungerstem projecting from a hardened waste mass is conspicuous evidence ofincomplete processing and, therefore the possibility of contamination.Other syringe parts can be used. Also in accordance with the invention,verifiability of sterilization of the waste mass after melt-down can beaugmented by the addition of or the intensification of pigmentation ofthe syringe part or parts selected for temperature-calibration. Theoptical characteristics of the solid waste mass, are discernablymodified when melt-down is complete; encapsulated needles can becomeless visible; and the waste mass can more easily be made self-labellingi.e. the manufacturer's name, trademark or logo can be made to appearconspicuously in the hardened waste mass. To this end a label of heatresistant material is applied to the syringe as a conventional statementof origin. It must be designed to endure the heat of subsequentprocessing and also to contrast with the pigmentation of the waste mass.For example, white, heat-resistant lettering in conjunction with a greyor black piston stem will be visible on the unused syringe, whether thelabel was applied directly to an outer surface of the transparent bodyportion or directly to the darker stem.

When a single syringe is melted down and hardened the waste mass in lumpform will take on a generally dark optical characteristic even thoughthe different plastics, opaque and transparent, of which the syringe isformed do not blend as would a dye for example, in water. Thelight-colored temperature-resistant label survives melt-down and willnot disappear into the dark but will remain visible and contrasting withthe dark even if encapsulated within transparent plastic. If manysyringes are melted down at once, many more or less discrete darkglobules will be dispersed throughout the mass to influence strongly theoptical characteristics of the whole as a generally dark mass; manylabels will show and few encapsulated needles can be perceived.

The process for melting down the syringes can be tailored to the numberof syringes in the load. For processing say 1 to 4 used syringes a smallcrucible in the shape of an inverted blunted cone is effective toconcentrate the molten plastic in a small conical lump of sufficientheight to bury the needles. Larger volumes can be processed in generallycylindrical crucibles. Liquefaction from the bottom up is accomplishedby using a temperature regulated heating plate at the bottom, contouredto receive the base of the crucible and providing a shielding baffleabove the plate to restrict the height of the heated area of thecrucible. Cooling can be provided above the baffle to maintain the uppercrucible walls at temperatures below liquefaction, allowing the syringesto sink into the mass without a film or flashing of plastic solidifyingon the wall. A fitted cover releasably clamped and carrying a filter forany gases which might be generated complete the processing assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in side elevation of a disposable hypodermic syringeembodying one form of the invention;

FIG. 2 is a view in vertical section of apparatus for processing thesyringes;

FIG. 3A is a view in perspective of a lump of improperly processed wastefrom two syringes conspicuously revealing by its geometry and otherphysical characteristics that processing was imperfect and sterilitycannot be verified;

FIG. 3B is a view in perspective corresponding to FIG. 3A in whichprocessing to the point of verification of sterility has been achieved.

FIG. 4A is a view in perspective of a waste mass which is the result ofimperfect processing in a large cylindrical crucible of a plurality ofsyringes; and

FIG. 4B is a view in perspective corresponding to FIG. 4A in which theoverall appearance and geometry verifies sterility and the harmlesscharacter of the waste.

Referring to FIG. 1 the invention in a preferred form is embodied in adisposable hypodermic syringe 10, one of many types sold worldwide, inwhich most of the structure is formed of thermoplastic such aspolyethylene or polypropylene formulated to become moldable under heatfor processing by various die and molding techniques. The syringe 10 isfor purposes of illustration, a design widely used by diabetics for theself-administration of insulin and as such constitutes a significantsource of contaminated but functional syringes which find their way,properly or improperly into the regular channels of refuse collection,recycling and dumping which are not in any event suited for handlingmedical waste.

The syringe 10 comprises a hollow cylindrical body or barrel portion 11to contain liquid medicaments and formed of transparent thermoplasticthrough which the liquid can be observed. A lubricated, resilientplunger or piston 12 often formed of a rubber compound slides in thebarrel under the control of an attached plunger stem 13 having athumb-actuator 14 operated in conjunction with an overhanging fingergrip 15 to cause liquid to pass through the hollow metal needle 16. Theneedle is held in a bead or ferrule 16a secured to a hub or adaptor 16battached to the barrel 11 so that the inner projecting end of the needleis in communication with the liquid chamber 17.

The thermoplastic hollow barrel 11 has relatively thin transparent wallsand carries indicia 18a operative in conjunction with the plunger 12 toenable metering of the medication. Identification labelling 18b such asa trademark, grade mark or logo reflecting the origin of the product isformed, in accordance with the invention, of heat resistant materialcapable of sustaining its integrity and legibility under the heat whichmelts the substrate on which it is carried. Labels 18b can be affixedfor example to the barrel 11, the actuator 14, the stem 13, or the hub16b of the syringe. The coloring of the labelling is important inrelation to the coloring and other optical characteristics of thesyringe before and after melt-down, all as described below.

The thermoplastics of which disposable syringes are formed have fullflow melting temperatures in the range of 130° to 150° C. In accordancewith the invention at least a portion of the syringe, for example, oneor more parts among the stem 13, actuator 14 and hub 16b, are formed ofa temperature-calibrated plastic having full flow melting temperaturesabove and differing substantially from those of the remaining, if any,syringe parts. The entire syringe including the body portion or barrel11 can be formed of such material but for a number of reasons, includingtransparency, is a less desirable part. The temperature of liquefactionselected for processing is a parameter which must be respected toprevent vaporization, burning and other environmentally adverse effectsduring processing as waste. Temperatures in the range of 180° to 200° C.have been found acceptable for practicing the invention using presentlyavailable materials.

Other desirable features of the temperature-calibrated plastic are safetoxological and ecological characteristics and increased crystalinity,the latter yielding snap phase changes between solid and liquid. Asaturated linear copolyester such as that sold under the trademarkDYNAPOL is an example of the thermoplastic useful in the practice of thepresent invention. Others are available or can be formulated. Examplesof the use of the effects of the temperature calibrated plastic invarious parts of the syringe are described below. It should be notedthat syringes are relatively small devices with relatively small massesof material being required for fabrication. Syringe parts will,therefore, melt relatively quickly so that the designer of aself-sterilizing syringe in accordance with the invention has a muchlower minimum possible time factor to work with than does the designerof a sterilizing system in which more massive charges oftemperature-calibrated plastic can be used.

The stem 13, which is out of contact with the liquids in the syringe,preferably includes relatively dark pigmentation achieved for example bycarbon black which can be tempered with white to form a grey whichcontrasts to the rest of the syringes and is capable of modifying theappearance of the final waste product when the syringe is melted down toproduce a self-sterilized, self-verifying mass encapsulating the needle.

The pigmentation is also selected to contrast with a label 18b which isapplied to the actuator 14 or the outside wall of the syringe barrel 11or both. In accordance with the invention the label 18b can be coloredwhite to contrast with the darker pigmented stem. It can also be applieddirectly to the stem, or to other parts such as the hub 16b but in allcases it should be made of a material which maintains its integrity andappearance through the highest possible temperature to which the syringewill be subjected in the thermal process. Thermosetting inks and paints,for example, can be used. The mechanics of the label reappearing in thefinal waste mass after melt-down are described below in conjunction withthe melt-down process.

Referring to FIG. 2, two used contaminated syringes 10 are shown in arelatively small thermal processor 19 having a contoured, melt-downcrucible 20 formed for example of teflon-lined drawn aluminum forreceiving the syringes. An inverted conical configuration with a bluntedapex 20a will concentrate the final mass into a lump of sufficientheight to exceed the needle length to ensure encapsulation. The lowerend 20a of the crucible 20 is received in a contoured heating plate 21of substantial mass for heat regulation and concavely contoured to matchthe crucible geometry. An electrical resistance heater 21a under thecontrol of a thermostat 22a and timer 22b provide the heat source forthe plate 21. A cover portion 23 containing a filter 24 is latched inplace in a gas tight seal over the crucible by a pivotally mountedhandle or bail 25 which releasably latches over the filter. An internalbaffle plate 26 with a resilient seal 27 engages the crucible near itslower end to confine convection currents to the lower end. Cooling vents28 are provided for the space above the baffle plate. If desired abi-metal flapper valve (not shown) can be provided in the baffle toclose automatically during the heat cycle and to open during the coolingcycle. Thus the waste load melts from the bottom up while the upper areais kept cool, preventing molten plastic from being wiped onto the upperwalls of the crucible and creating troublesome flashing.

The time frame within which the temperature-calibrated plastic changesphase in the shortest theoretically possible interval and thetemperature reached are the two variables which position the process onthe time-death curve for microbial life. See "Disinfection,Sterilization and Preservation: by Seymour S. Block, Lea and Fibger1993, which establishes that within stainless steel surfaces (anexperimental model for the space within a hollow hypodermic needle) atemperature of approximately 190° C. achieves instantaneous death. Astemperature declines, the time in which total death occurs rises sorapidly it is often shown on a logarithmic scale. Below 150° C. the timereaches so many hours that it is no longer an option for sterilizationprocesses.

In accordance with the invention, therefore, a determination must bemade of the least possible time within which melt-down andresolidification of the waste mass (two successive phase changes) canpossibly occur, given the most time-and-thermal efficient heat exchangemethods and apparatus known, and working within vapor temperature limitsthat preclude serious vaporization, gassing off, or even ignition of thewaste.

The form factor of the part or parts made of temperature-calibratedplastic plays a part in the equation, with a thin, sheet-like memberwith large exposed surface areas having a shorter time constant forphase change than, say, a solid cylindrical member such as the stem 13.

Whereas it is a relatively simple matter to melt down a conventionaldisposable thermoplastic syringe and to solidify it into a lump withoutsterilizing i.e., reaching the time-death curve, a design using theprinciples of the invention can provide a syringe that cannot be melteddown and solidified into a lump without achieving sterilization. It ispossible to design a syringe in which sterilization is necessarilyachieved at the instant of melt-down, with any time that follows being asafety factor.

Moreover, the invention provides for visual verification of anunsterilized waste mass. If the syringe 10 is processed at a temperaturesetting of say 155° C. for enough time (plus any amount more time) tomelt down the syringe barrel into a lump as shown in 3A, thetemperature-calibrated plastic stem 13 and actuator 14 will survive asan indicator of non-sterility. On the other hand, if the process iscarried out in the fastest way possible to achieve melt-down of the stemand actuator and then solidification as shown in FIG. 3B, the time-deathcurve will have been exceeded and sterility assured. It should also benoted that it is possible to achieve sterilization of the mass withoutmelting the stem and actuator. If for example, the waste is heated to160° for, say, half an hour, achieving melt-down of all but the stem andactuator, the appearance of FIG. 3A will result even though the mass issterile. But a half-hour is a finite time, and 160° a finite temperatureboth of which are unverifiable by the appearance of the final product.Time and temperature of themselves are unverifiable functions after thefact; the best clocks and the best thermometers can break down even inthe hands of the most reliable operator, and the end product will notreadily reflect the error. The temperature calibrated plastic is notsubject to these problems; if it has not melted, infection can bepresent; if it has melted microbial infectious matter cannot be presentwithin the mass. If the temperature-calibrated plastic has beenerroneously calibrated, whether deliberately or intentionally, itremains in the waste to reveal the error.

It is possible as well as desirable, therefore, to provide labellingwhich follows the syringe from its inception through the thermalprocessing. The label 18b being impervious to the heat will survive inthe mass 29 of FIG. 3A. The white indicia will be somewhat visible inthe more or less transparent lump 29, effected optically only by theplungers 12 at the ends of the stems 13. The needles 16 are alsovisible. In FIG. 3B, however, the entire lengths of the pigmented stems13 have become two large randomly shaped dark masses within the lump.Although not fully blended, they constitute a relatively largepercentage of the whole even though partly immersed in the transparentplastic of the body portion. Optically, the mass appears essentiallydark. The white indicia 18b in the generally dark mass will not exceptin rare cases be obscured but will stand out in contrast to it. Theindicia on the actuator 14 will almost always appear on the top surfaceof the processed lump. Thus, the origins of the temperature-calibratedplastic and the syringes themselves can be traced. The needles will berelatively obscured.

Referring to FIGS. 4A and 4B there are illustrated solidified wastemasses 30 and 31 which are the result of processing in generallycylindrical crucibles (not shown) of a plurality of syringe 10, say onthe order of fifty. The lump or mass 30 is primarily clear ortransparent plastic with stems 13 and actuators 14 projecting randomly.Needles 16 and pistons 12 can be perceived as can to some extent thelabels 18b. Sterility is possible but in no way certain or verifiable.In FIG. 4B the myriad of more or less discrete dark amorphous shapes sopermeate the whole that optically it is perceived as more or lessuniformly dark. The needles 16 are less visible; the black pistons 12blend in; and the white labels 18b stand out conspicuously at manypoints at any angle of view. The mass 31 is verifiably sterile,harmless, and no longer constitutes Regulated Medical Waste.

As disclosed above, it is also possible to fabricate the hubs oradapters 16b of temperature-calibrated plastic. This mode of theinvention differs from that in which the stem 13 is formed oftemperature-calibrated plastic. Referring to FIG. 2, it will be seenthat the used syringes are standing on their needles 16 with the needlesbeing held by their hubs 16b. The heat at the base of the crucible willconduct upward through the needles and the hot air will convect upward.If the temperature is below that called for to achieve verifiablesterilization, the hubs 16b will not melt, either by conduction orconvection. It will take a long time for the body or barrel 11 to softenand melt, if at all, giving the operator evidence that the thermostat,for example, may have malfunctioned. If the barrel eventually melts downand if the needles hold firm in hubs (it is possible to render themreleasable by using meltable plastic seals or ferrules 16a or to renderthem fixed by using, for example, metal ferrules) the combined length ofthe exposed needle and the hub will project above the rest of the melteddown syringe, assuming the stem and actuator are formed of conventionalsyringe plastic. The length of hubs without the needle extension isnormally sufficient to exceed the height of the solidified lump. Thus,evidence of possible failure to sterilize is presented to the operatorand others in the waste handling chain. This feature is not available ina system in which a large number of syringes is placed in a widecylindrical crucible where they can become horizontal; it is most usefulwhen one or two syringes are melted down in the small, contouredcrucible 20.

While the invention has been disclosed above, referring to preferredembodiments, it will be understood that it can take other forms andarrangements without departing from the scope of the invention. Forexample, the labels 18b can be made dark and the stem 13 pigmented inwhite to contrast. Also, more sophisticated temperature controls can beused for the processor to speed processing. Since the needles 16initially hold the syringes from the crucible walls (see FIG. 2), theinitial temperatures can be set higher, well into the range at whichburning and gassing of the plastic and rubber pistons would normallyoccur, and then subsequently lowered. Temperatures can also bemaintained higher while the phase change is occurring, with theaugmented heat absorption of liquefaction of the plastic preventing theplastic mass from reaching dangerous temperatures. Also, while theinvention has been described having reference to thermoplastichypodermic syringes, it is applicable to other thermoplastic medicalhypodermic devices such as disposable scalpels in which the handle canbe temperature-calibrated plastic, the melt-down of which can verify thesterilization of the blade and, when provided in sufficient volume,encapsulation of the blade. The invention should not therefore beregarded as limited except as set forth on the following claims.

What is claimed is:
 1. A thermal processor for melting and solidifyingmaterials including thermoplastic in conjunction with medical waste,said processor comprising:a housing having an upper end and a lower end;a controllable heat source adjacent to the lower end of the housing; aheat resistant container removably mounted in the housing and adapted toreceive the materials for processing, said container having sides, anupper end and a lower end; a controllable heat source disposed below thecontainer to apply heat to the lower end thereof; and a baffle meansdisposed within the housing to engage the sides of the containeradjacent its lower end to define a hot chamber between the baffle andthe heat source and a cool chamber above the baffle.
 2. A thermalprocessor as set forth in claim 1, further comprising vent means formedin said housing above the baffle means, said vent means being incommunication with said cool chamber to establish a flow of unheated airon the container.
 3. A thermal processor as set forth in claim 1,wherein said container is formed with a relatively wide mouth at theupper end and wherein said sides are formed as downwardly convergentwalls to define a relatively small volume to concentrate moltenthermoplastic to encapsulate unmelted medical waste.
 4. A thermalprocessor as set forth in claim 1 including a detachable cover portion,a filter in said cover portion, and a U-shaped locking member pivotallymounted on the housing at diametrically spaced points to be swung upwardabove the cover portion to engage the filter.